Re: [PATCH v4 12/38] ALSA: pcm: use vm_insert_page() to map PCM status page
flat view
From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-10-04 17:23:04
Also in:
bpf, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fbdev, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-trace-kernel, linux-usb, lkml, selinux, sparclinux
On Sat, Oct 3, 2026 at 6:37 PM Lorenzo Stoakes (ARM) [off-list ref] wrote:
There's no need to keep a fault handler around for this, instead map on mmap. While we're here, rename area to vma to be consistent. This correctly makes the mapping a mixed map mapping. This works towards establishing the invariant that only PFN mapped or mixed map mappings may clear the VM_MAYWRITE flag. The status page mapping clears VM_MAYWRITE, so it must not be mm-managed; the control page mapping remains writable and is left fault-based. The assumption is made that the struct pcm_mmap_status structure is at most a page in size, which is asserted as a build bug. This is safe to assume, as the size of the structure is 56 bytes at most. Acked-by: Takashi Iwai <redacted> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
quoted hunk ↗ jump to hunk
--- sound/core/pcm_native.c | 38 +++++++++++++------------------------- 1 file changed, 13 insertions(+), 25 deletions(-)diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 62324282fcae..c98fb3df14f3 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c@@ -3760,39 +3760,27 @@ static __poll_t snd_pcm_poll(struct file *file, poll_table *wait) /* * mmap status record */ -static vm_fault_t snd_pcm_mmap_status_fault(struct vm_fault *vmf) +static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file *file, + struct vm_area_struct *vma) { - struct snd_pcm_substream *substream = vmf->vma->vm_private_data; + const unsigned long size = vma->vm_end - vma->vm_start; struct snd_pcm_runtime *runtime; - - if (substream == NULL) - return VM_FAULT_SIGBUS; - runtime = substream->runtime; - vmf->page = virt_to_page(runtime->status); - get_page(vmf->page); - return 0; -} + struct page *page; -static const struct vm_operations_struct snd_pcm_vm_ops_status = -{ - .fault = snd_pcm_mmap_status_fault, -}; + BUILD_BUG_ON(sizeof(struct snd_pcm_mmap_status) > PAGE_SIZE); -static int snd_pcm_mmap_status(struct snd_pcm_substream *substream, struct file *file, - struct vm_area_struct *area) -{ - long size; - if (!(area->vm_flags & VM_READ)) + if (!(vma->vm_flags & VM_READ)) return -EINVAL; - size = area->vm_end - area->vm_start; - if (size != PAGE_ALIGN(sizeof(struct snd_pcm_mmap_status))) + if (size != PAGE_SIZE) return -EINVAL; - area->vm_ops = &snd_pcm_vm_ops_status; - area->vm_private_data = substream; - vm_flags_mod(area, VM_DONTEXPAND | VM_DONTDUMP, + + vm_flags_mod(vma, VM_DONTEXPAND | VM_DONTDUMP, VM_WRITE | VM_MAYWRITE); + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); - return 0; + runtime = substream->runtime; + page = virt_to_page(runtime->status); + return vm_insert_page(vma, vma->vm_start, page); } /* --2.55.0